change an image from rectangular to square by adding white area

Dears, i have a dataset that im working on but all of them in rectangular shape, i wand them to be square by adding white area ( raws or coloumns depending on the image) many thanks in advanced

[Rik]

What have you tried so far? This type of padding should not be too hard. Note that the value that you need to add may depend on the data type and value range of the image.

[hamsa dhia]

i tried this code but it add black margin to the image , i need to fill the lack of pixels in white not black please

im = imread('1.jpg');
nrows = size(im,1);
ncols = size(im,2);
d = abs(ncols-nrows);    % difference between ncols and nrows:
if(mod(d,2) == 1)        % if difference is an odd number
    if (ncols > nrows)   % we add a row at the end
        im = [im; zeros(1, ncols)];
        nrows = nrows + 1;
    else                 % we add a col at the end
        im = [im zeros(nrows, 1)];
        ncols = ncols + 1;
    end
end
if ncols > nrows
    im = padarray(im, [(ncols-nrows)/2 0]);
else
    im = padarray(im, [0 (nrows-ncols)/2]);
end
figure; imshow(im)

Answer 1

[Rik]

The documentation for padarray states it will pad with 0. If you don't want that, you will have to provide the value as the third argument. You probably want 255, but you can use the code below to determine that dynamically.

switch class(im)
    case 'uint8'
        padval = uint8(255);
    case 'double'
        padval = 1;
    otherwise
        error('check what value you need')
end

Edit: a much better solution that this code is to use the function that @DGM showed in his answer: getrangefromclass.

range = getrangefromclass(im)
padval = range(2);

[hamsa dhia]

unfortuenatly not working , the black are still there i want them white

[Rik]

What intensity value does the white part have in your image?

[hamsa dhia]

still not working :(

Answer 2

[DGM]

I don't normally use getrangefromclass(), but that's one way to get the white value. Of course, it's impossible to tell that the result is padded here because it's displayed on a white background

inpict = imread('peppers.png');
%inpict = rot90(inpict); % will pad either dimension

outpict = squarewhitematting(inpict);
imshow(outpict)

function outpict = squarewhitematting(inpict)
% add symmetric white padding to the smaller dimension of the image geometry
% so that the resulting image is square
% INPICT is an image of any standard image class, with any number of channels.
% multiframe images are supported

    % get nominal black and white value
    valuerange = getrangefromclass(inpict);
    
    [h,w,~] = size(inpict);
    if h == w
        % nothing to do
        outpict = inpict;
        return;
    else
        if w > h % wide image; pad top/bot
            padamt = [(w-h)/2 0];
        else % tall image; pad l/r
            padamt = [0 (h-w)/2];
        end
        
        % use floor/ceil to deal with odd differences
        outpict = padarray(inpict,floor(padamt),valuerange(2),'pre');
        outpict = padarray(outpict,ceil(padamt),valuerange(2),'post');
    end
end

[Rik]

If you use this code instead of imshow you can verify that there is a white border added.

image(outpict),daspect([1 1 1])

[DGM]

That's a good point

[hamsa dhia]

this line gives error

image(outpict),daspect([1 1 1])

this line is worked

imshow(outpict)

thank you so much for you both

[Rik]

Something strange is going on if that line doesn't work. image is the primitive that is called by imshow (just like plot calls line and surf calls patch).

But if you have a working solution now, that should do it. There is no fundamental difference between the code I suggested and what DGM implemented (other than that DGM provided you with a full implementation).